References of "Gaydardzhiev, Stoyan"
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See detailImproving the grinding performance in ball mills with a conductive and inductive sensor
Köttgen, Axel ULg; de Haas, Bernard; Keshav, Pratish et al

Poster (2010)

A series of tests were conducted in a South African concentrator on the secondary grinding mill. The results were analysed and provided showed the importance of selecting an optimum density and filling ... [more ▼]

A series of tests were conducted in a South African concentrator on the secondary grinding mill. The results were analysed and provided showed the importance of selecting an optimum density and filling degree of the mill. Moreover, a Sensomag (r) is installed on this mill and the surveys showed that an increase of the density was improving the mixing of balls in the pulp and increasing the grinding performance. [less ▲]

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See detailBacterial leaching of complex sulphides from mine tailings altered by acid drainage
Kitobo, Willy; Gaydardzhiev, Stoyan ULg; Frenay, Jean ULg et al

in Dominic, Esteban (Ed.) Bacterial leaching of complex sulphides from mine tailings altered by acid drainage (2009, May)

An experimental study aimed at re-flotation of laid down tailings from Kipushi (DRC) to bring sulphide concentrate suitable for further processing by hydrometallurgical means has been realized. The ... [more ▼]

An experimental study aimed at re-flotation of laid down tailings from Kipushi (DRC) to bring sulphide concentrate suitable for further processing by hydrometallurgical means has been realized. The results from a bioleaching route chosen to accomplish the later task by use of moderate thermophilic and mesophilic microorganisms are reported. It has been found that due to the complexity of the treated material, the leaching pattern of the two principal metals of interest, copper and zinc vary. Whilst the copper bearing minerals have been leached relatively fast by direct mechanism, the leaching kinetics for the zinc minerals has been moderate involving predominantly an indirect mechanism. The effects of pH and temperature variations and ferrous ions addition upon the extent of copper and zinc dissolution have been examined. The presence of ferrous ions has been found beneficial for the leaching of sphalerite, however the concomitant formation of jarosite precipitates has led to copper leaching hindrance. Similarly, the rapid zinc solubilisation has been counterbalanced by decrease in rate of copper dissolution. [less ▲]

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See detailFibrous natural materials for ceramic processing
Gaydardzhiev, Stoyan ULg; Wilker, Viola; Scheffler, Michael

in Zuo, Wang (Ed.) Proceedings of the XXIV International Mineral Processing Congress (2008, September)

Initial experiments towards preparation of hollow ceramic microtubes by dip-coating of fibrous plants with water based alumina gel-casting slurries using hemp and coconut fibres as templates have been ... [more ▼]

Initial experiments towards preparation of hollow ceramic microtubes by dip-coating of fibrous plants with water based alumina gel-casting slurries using hemp and coconut fibres as templates have been done. It has been found that the wettability of fibres and accordingly the stability of the developed ceramic layer on their surface during slurry gelation varied significantly within the different fibre types. Good correlation between the diameters of the template fibres and the resulting channels has been found at the 31 % solids loadings level. Hemp fibres used as bundles have led to formation of multi channel patterns while the coconut fibres-templated process resulted in uniform monochannel materials. The micro tubes have shown good mechanical handling properties. [less ▲]

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See detailDip-coating of fibrous natural materials for alumina tube manufacturing
Gaydardzhiev, Stoyan ULg; Wilker, Viola; Scheffler, Michael

in Advanced Engineering Materials (2008), 10(3), 223-226

Results from preliminary studies for development of hollow ceramic tubes by dip-coating of fibrous plants with water based gel-casting slurries are presented. Hemp and coconut fibres have been tested as ... [more ▼]

Results from preliminary studies for development of hollow ceramic tubes by dip-coating of fibrous plants with water based gel-casting slurries are presented. Hemp and coconut fibres have been tested as templates reflecting in different macro and micro structures of the obtained ceramic tubes. Good correlation between the diameters of the template fibres and the developed channels has been documented, the ordering of the channels inside the tubes being function of the mode of fibres implementation: as singles or as bundles. By coating hemp fibres in bundle, multi channel pattern has been developed, resulting from splitting of the bundle. By using single coconut fibre as template, uniform mono channels with 250 – 400 µm in diameter were observed. The developed tubes have been characterized by good end finish. The observed differences in their microstructure offer possibilities for adjusting the physical properties towards prospective application niches. [less ▲]

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See detailGel-casted porous Al2O3 ceramics by use of natural fibres as pore developers
Gaydardzhiev, Stoyan ULg; Gusovius, Hans; Wilker, Viola et al

in Journal of Porous Materials (2007)

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See detailCharacterisation of stability behaviour of ultra fine alumina powder in view its colloidal processing by gel-casting
Gaydardzhiev, Stoyan ULg; Ay, P.

in Onal G. et al. (Ed.) Proceedings of XXIII International Mineral Processing Congress, 3-8 September 2006, Istanbul (2006, September)

The paper reports on results study aimed at assessing of the influence of dispersant type on the electrochemical properties of highly concentrated alumina suspension. The relationship between the type of ... [more ▼]

The paper reports on results study aimed at assessing of the influence of dispersant type on the electrochemical properties of highly concentrated alumina suspension. The relationship between the type of dispersant and the stabilization ability towards ultrafine alumina powder CT3000 has been studied. The effectiveness was determined mainly by the zeta potential value, specific surface charge, the shift in the pH(iep) and by visual controlling the fluidity of the slurry at constant solid loading. A good agreement between the zeta potential and the specific surface charge as a way to determine the optimal dose of dispersant has been documented. Gel-casting experiments showed that the Dolapix CE64, an ammonium polyacrylate dispersant was the best dispersant for the studied powder. [less ▲]

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See detailRemoval of selected azo dyes from textile wastewater by chemical coagulation/flocculation: implication of the dye destabilization mechanism
Janeczko, M.; Gaydardzhiev, Stoyan ULg; Ay, P.

in Fecko P et al. (Ed.) Proceedings of 10-th Conference on Environment and Mineral Processing (2006, June)

The results of the coagulation/flocculation of six commercially used textile azo dyes coagulated with synthetic primary coagulants are discussed in the paper. Surface charge measurement of coagulated dye ... [more ▼]

The results of the coagulation/flocculation of six commercially used textile azo dyes coagulated with synthetic primary coagulants are discussed in the paper. Surface charge measurement of coagulated dye-flocs was employed to find a correlation between its sign and the level of colour removal. Additionally, flocs characterization was done with the aim to link data with surface charge and on this basis to outline the predominant mechanism of colour removal. Based on the results obtained, the evident correlation between surface charge density progression of coagulated dye flocs and colour removal after different solid/liquid separation methods was observed. Thus, it was concluded that the charge neutralization was the predominant mechanism responsible for dye destabilisation. It was found out also that flocs produced at optimal dosage are characterized by large median size and high value of fractal dimension [less ▲]

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See detailRemoval of dyes from textile wastewater by chemical coagulation
Janezcko, Marta; Gaydardzhiev, Stoyan ULg

in Önal, G. (Ed.) XXIII International Mineral Processing Congress, 3-8 September 2006, Istanbul (2006)

Dye removal mechanisms from textile effluents has been studied by means of surface charge measurempents and image analysis of floc sludge (size, shape, sedimentation properties). Reactive Black 5 and Acid ... [more ▼]

Dye removal mechanisms from textile effluents has been studied by means of surface charge measurempents and image analysis of floc sludge (size, shape, sedimentation properties). Reactive Black 5 and Acid Black 1 commercial dyes have been tested as simulated effluent water solutions treated with synthetic primary coagulants. [less ▲]

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See detailColour removal from wastewater by means of microbial treatment
Janeczko, M.; Georgiev, P.; Nicolova, M. et al

in Fecko, P. (Ed.) 10-th Conference on Environment and Mineral Processing (2006)

Water solutions of different dyes used in textile industry (Reactive Black 5, Acid Orange 7 and Disperse Yellow 5) were treated under laboratory conditions by means of different microorganisms or their ... [more ▼]

Water solutions of different dyes used in textile industry (Reactive Black 5, Acid Orange 7 and Disperse Yellow 5) were treated under laboratory conditions by means of different microorganisms or their metabolites. The following organisms were used in this study: Bacillus megatherium, B.subtilus, B.circulans, activated sludge from industrial w. w. teratment plant and a mixed enriched culture of flocculating bacteria. It was find out that the microbial effect towards the dyes was quite specific and the extent of colour removal varied in broad range. Very good results were achieved also by means of permeable reactive barriers inhabitated by flocculating bacteria and other independent microorganisms and operating under continuous flow conditions. The colour removal in these case varied in the range of about 80 - 90 % and was similar to that achieved by the well known chemical reagents used in the textile industry. [less ▲]

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See detailComparative studies of dispersant optimisation techniques for evaluating the stability of concentrated alumina slurries
Gaydardzhiev, Stoyan ULg; Ay, Peter; Janeczko, Marta

in Particle & Particle Systems Characterization (2006), 23

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See detailSize and structure characterization of dye flocs during chemical coagulation of Reactive Black 5 dye
Janeczko, Marta; Gaydardzhiev, Stoyan ULg

in Particle & Particle Systems Characterization (2006), 23

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See detailStabilization of aqueous silicon nitride suspension with Dolapix A 88
Singh, Bimal; Gaydardzhiev, Stoyan ULg; Ay, Peter

in Journal of Dispersion Science & Technology (2006), 27(1), 91-97

The dispersing phenomenon of silicon nitride suspension has been investigated systematically by measuring surface charge density, sediment volume and turbidity of the suspension. Dolapix A 88 has been ... [more ▼]

The dispersing phenomenon of silicon nitride suspension has been investigated systematically by measuring surface charge density, sediment volume and turbidity of the suspension. Dolapix A 88 has been used as dispersant to improve the stability of the suspension and assessed through measurement of the specific surface charge of the Si3N4 system. The isoelectric point (iep) of Si3N4 powder has been found to be at pHiep = 6.91 and there was no shift in iep due to presence of dispersant indicating that the interaction between the powder and the dispersant Dolapix A88 is purely physisorbing in nature. Good agreement has been observed between dispersion characteristics, surface charge and streaming potential inflection. The paper also describes the selection and optimisation of the dispersant in controlling stability of an aqueous suspension of Si3N4. It can be concluded from this investigation that the PCD technique for measurement of specific surface charge can be conveniently used for the assessment of dispersibility of ceramic suspension in both dilute as well as in concentrated suspensions [less ▲]

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See detailCharacterisation of aqueous suspensions of fumed aluminium oxide in presence of two Dolapix dispersants
Gaydardzhiev, Stoyan ULg; Ay, Peter

in Journal of Materials Science (2006), 41

The stability of a fumed aluminium oxide nano powder suspended in water has been assessed through measurement of zeta potential and streaming current, using the fact that the particles exhibit maximum ... [more ▼]

The stability of a fumed aluminium oxide nano powder suspended in water has been assessed through measurement of zeta potential and streaming current, using the fact that the particles exhibit maximum repulsion at high magnitude of charge. Two commercial dispersants belonging to a Dolapix series have been tested. Dolapix CE 64 has shown a better deflocculating action than Dolapix A 88. The iso electric point of the powder suspension has been found close to pH 9. A notable shift in the pH of iso electric point when Dolapix CE 64 was present, indicating that the interaction between particles and dispersant has involved chemical sorption. It has been found out, that at the relative low solids loading studied and within the limits of the pH measurement accuracy, a dispersant supplied in dose levels from 12 to 24 mg/g, has confined the pHiep to a relatively narrow range. A capillary suction time technique has been tried for evaluation of suspension fluidity as function of dispersant concentration and pH. For the dispersant stabilised suspensions, a correlation between their CST and pHiep has been documented [less ▲]

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See detailEvaluation of dispersant efficiency for aqueous alumina slurries by concurrent techniques
Gaydardzhiev, Stoyan ULg; Ay, Peter

in Journal of Dispersion Science & Technology (2006), 27(3), 413-417

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See detailColour removal from model solutions by coagulation - surface charge and floc characterisation aspects
Gaydardzhiev, Stoyan ULg; Karthikeyan, J.; Ay, P.

in Environmental Technology (2006), 27

Chemical coagulation applied for colour removal from dye bearing solutions has been investigated from point of view of surface charge progression. Two commercially used dyes, i.e. CI Acid Blue 113 and CI ... [more ▼]

Chemical coagulation applied for colour removal from dye bearing solutions has been investigated from point of view of surface charge progression. Two commercially used dyes, i.e. CI Acid Blue 113 and CI Disperse Blue 26 have been tested, employing three common coagulants: alum, aluminium chloride and ferric chloride. Coagulant type and dose level and pH of the dye solution have been studied as process parameters affecting surface charge and degree of colour removal after filtration of coagulated dye. It has been found, that both dyes could be almost completely removed with the tested coagulants, when supplied however at different dosages. From one side, the correlation between surface charge and colour removal suggests that destabilization of colour colloids occurs as a result of charge neutralization followed by removal by filtration. From other side, the lack of re-stabilization and continued high colour removal even at increased coagulant dosages implies enmeshment of destabilized dye colloids into the hydroxy flocs/precipitates of metal coagulant by “sweep coagulation”. Finally, flocs from selected sludge samples have been examined for particle size and shape by image analysis and their key characteristics summarised [less ▲]

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See detailImplication of surface charge effects in color removal from effluents by chemical coagulation - the case of CI Reactive Blue 4 dye
Gaydardzhiev, Stoyan ULg; Ay, Peter

in Pratsinis, S. (Ed.) Proceeedings CD of Partec 2004 Inetrnational Congress of Particle Technology (2004, March)

Characterisation of dye flcos during colour removal from synthetic waste water is presented. Surface charge and floc size and shapes are measured and an implications towards the predominant removal ... [more ▼]

Characterisation of dye flcos during colour removal from synthetic waste water is presented. Surface charge and floc size and shapes are measured and an implications towards the predominant removal emchanisms is made. [less ▲]

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See detailMineralogical characteristics of copper flotation products from Cayeli mine, Turkey and their influence to mineral processing
Strashimirov, S.; Dobrev, S.; Stamenov, S. et al

in Annual of the University of Mining and Geology, Sofia, 47, I, 147-153 (2004)

The paper presents mineralogical characteristics and pecularities of minerals distribution in products from Cu cycle of clastic ore mineral processing in Cayeli concentrator, Turkey. Special attention has ... [more ▼]

The paper presents mineralogical characteristics and pecularities of minerals distribution in products from Cu cycle of clastic ore mineral processing in Cayeli concentrator, Turkey. Special attention has been drawn to the mineralogical pecularities of sphalerite. The study has covered 16 samples from Cu flotation feed, Cu rougher concentrate, Cu final concentrate and tailing, each sieved in 4 granulometric classes. Significant quantity of sphalerite charactarized by higher amount of Cu and Fe as isomorphic impurities or extemely fine crystals of chalcopyrite are present in the Cu concentrate. Based on the performed studies, an improvement in the processing circuit has been suggested - especially in the grinding and hydrocycloning circuits. [less ▲]

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See detailSurface charge studies - an important approach for investigation of color removal from textile wastewaters by chemical coagulation
Gaydardzhiev, Stoyan ULg; Ay, P.

in Rao; Misra (Eds.) MPT 2004 Conference Proceedings (2003)

Results concerning surface charge characterizations of coagulated dye with an aim to evaluate the predominant destabilization mechanism taking place during colour removal by chemical coagulation are ... [more ▼]

Results concerning surface charge characterizations of coagulated dye with an aim to evaluate the predominant destabilization mechanism taking place during colour removal by chemical coagulation are presented. A model wastewater comprising of commercially used dye with a CI “Reactive Red 2” was studied. The effect of the combination coagulant/flocculant on colour removal by filtration and sedimentation was evaluated in terms of progression of sludge surface charge. On that basis, an implications about the predominant colour removal mechanisms have been drawn. On selected sludge samples, floc characterisations in terms of size by laser scattering and shape were performed. The measurement techniques used have encompassed for particle size and Small Angle Light Scattering (SALS) for fractal dimension. [less ▲]

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See detailImprovement of a syllabus on environmental protection designed for mineral and mining engineering students in Bulgaria
Gaydardzhiev, Stoyan ULg

in 6th International auDes Conference Bridging Minds & Markets, Venice, 5 – 7 April 2001 (2001)

The University of Mining and Geology in Sofia as a unique academic Institution engaged in training graduates to work in the field of mining and geological prospecting faces the need for modification and ... [more ▼]

The University of Mining and Geology in Sofia as a unique academic Institution engaged in training graduates to work in the field of mining and geological prospecting faces the need for modification and updating its curriculum, for being able to meet the challenges of European educational standards like Institution accreditation, ECTS, etc. In a smaller scale, this is particularly relevant to the Department of Mineral Processing which is one of the largest Departments (in the University) and is engaged in training students for the entire raw materials (non-petroleum) industry: ores, coal and industrial minerals. Despite the drastic reduction in great number undergraduate specialisations, the specialization “Mineral Processing” remains in the Governmental Register released by the Ministry of Education, Science and Technologies. Therefore in this new situation, there is a necessity to verify and to parallel the existing syllabus to the one practiced in a similar Departments in the EU countries and more precisely to develop undergraduate and graduate courses to include risk and hazard assessment, environmental protection and related matters. [less ▲]

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See detailThiourea leaching of gold bearing mine wastes from Madjarovo processing plant in SE Bulgaria
Gaydardzhiev, Stoyan ULg

in Nath, B. (Ed.) Proceedings of NATO ARW “Sustainable Solid Waste Management in the Southern Black Sea Region”, September 1999, Sofia, Bulgaria (2000)

Flotation tailings derived from processing of complex sulphide gold-bearing ores have been repropcessed by means of thiourea leaching. Before leaching takes place the materials has been subjected to ... [more ▼]

Flotation tailings derived from processing of complex sulphide gold-bearing ores have been repropcessed by means of thiourea leaching. Before leaching takes place the materials has been subjected to magnetic separation, flotattion and hydrocloric leaching. An environmental and economic benefits could be expected provided the approach is implementyed on site. [less ▲]

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